Surge Arrester Resistive Leakage Current Tester: Function, Operating Principles, and Detailed Field Assessment Criteria

In a nutshell: The arrester resistive leakage current detector is a portable, live-line testing instrument designed to assess the condition of Metal Oxide Arrester (MOA) surge arresters—specifically detecting degradation or moisture ingress—while the equipment remains energized. It achieves this by separating the resistive component (Ir) from the capacitive component (Ic) within the total leakage current. This device serves as a standard tool for condition-based maintenance in substations operating at 110 kV and above.

Target Audience: Power maintenance personnel, electrical testing engineers, power equipment operation and maintenance teams, and substation duty officers.

1. The Arrester Resistive Leakage Current Detector is also known as the Zinc Oxide MOA Live-Line Tester or the ZXBLQ Zinc Oxide Arrester Tester.
2. The core problem it solves: Measuring only the total current fails to detect internal deterioration within the arrester.
3. Main Applicable Standards: DL/T 474.5-2013, Q/GDW 1168-2013, GB/T 11032-2020.

The Arrester Resistive Leakage Current Detector is a portable instrument specifically designed for the live-line testing of Metal Oxide Arresters (MOA). Its core function is to accurately separate the resistive component (Ir) and the capacitive component (Ic) from the total leakage current (total current Ix) flowing through the arrester—all while the main equipment remains energized. By analyzing the trend of the resistive component, the instrument assesses the internal health status of the arrester.

Common Industry Names: Zinc Oxide Arrester Live-Line Tester, Zinc Oxide Arrester Characteristic Tester, Zinc Oxide Arrester Resistive Current Tester, Arrester Resistive Leakage Current Detector, Zinc Oxide Arrester Live-Line Testing Instrument, Zinc Oxide Arrester Tester, Zinc Oxide Arrester Comprehensive Tester, Zinc Oxide Arrester DC Leakage Tester.

The core components of an MOA arrester are the Zinc Oxide (ZnO) varistors. Under the influence of multiple factors—such as prolonged operating voltage, lightning surges, internal overvoltages, and moisture ingress—these varistors undergo gradual deterioration. Once the varistors deteriorate to a critical level, thermal runaway may occur within a span of months, days, or even just a few hours. This triggers an explosive failure of the arrester, potentially leading to widespread power grid accidents.

The total leakage current (Ix) flowing through the arrester under operating voltage consists of two components:

Key Features: The operating voltage itself exhibits a fluctuation of ±5%, causing the total current to fluctuate accordingly. Even if the resistive component doubles, the magnitude of the change in total current remains very small—easily masked by the voltage fluctuations.

• Initial difference in resistive current ≤ 50%; initial difference in total current ≤ 20%
• If resistive current increases by 0.5 times → Shorten the test interval and intensify monitoring
• If resistive current increases by 1 time → Immediately de-energize and inspect

Measuring total current = Routine screening; Measuring resistive current = In-depth diagnosis. The former reveals only surface-level conditions, while the latter enables the precise identification of latent defects within the arrester valve elements.

• Q1: What is the difference between this and a standard leakage current monitor? Standard instruments measure only the total current and cannot separate it into resistive and capacitive components; a resistive current detector, however, can precisely isolate these two components, allowing for the detection of degradation at its earliest stages.
• Q2: Why is a DC voltage corresponding to 1 mA used as the reference? According to national and industry standards, the 1 mA point corresponds to the "knee" (inflection point) of an arrester's V-I characteristic curve; at this point, the parameters are stable, making it suitable for standardized benchmarking.
• Q3: What constitutes a normal resistive current level? A resistive current accounting for 10%–20% of the total current is considered normal; 25%–40% warrants close monitoring; and exceeding 40% suggests that the equipment should be taken out of service for evaluation. Furthermore, it is crucial to analyze the historical trend of these values.
• Q4: Can this device measure 10 kV distribution arresters? Technically, yes; however, in practice, this is rarely done. The leakage current in 10 kV systems is typically too low, making them more suitable for DC testing conducted while the power is de-energized.
• Q5: How often should measurements be taken? Typically, once per year as part of routine maintenance. Additional measurements should be performed before the summer peak-load season and after the thunderstorm season; furthermore, an inspection is mandatory whenever the arrester has discharged (operated). If the resistive current increases by more than 50%, the inspection frequency should be increased; if it doubles, the equipment must be immediately taken out of service for inspection.

Which model of arrester resistive leakage current detector does your organization use? What common issues have you encountered in the field? We welcome your comments and insights below.